1. Field of the Invention
The present invention relates to a fuel cell system and a method of activating a fuel cell.
2. Description of the Related Art
In a fuel cell which generates electric power through a reaction between reactive gases supplied thereto, if water is frozen in the fuel cell, passages are blocked or closed, which obstructs diffusion of the reactive gases and reduces the effective power generation area of the fuel cell. That is, in comparison to when operating at ordinary temperatures, consumption of the reactive gases is reduced, thereby degrading the performance of the fuel cell in generating electric power. Therefore, when the fuel cell is activated at a below-zero temperature, a specific activating operation for below-zero temperatures is executed so as to increase the temperature of the fuel cell and obtain the required ability of the fuel cell to generate electric power.
Conventionally, the temperature of the fuel cell is measured, and it is determined whether such a specific activating operation for below-zero temperatures is executed based on the measured temperature. When the specific activating operation is executed, the pressure for supplying the reactive gases or the amount of such gases is increased in comparison to when operating at ordinary temperatures. See, for example, Japanese Unexamined Patent Application, First Publication No. 2005-44795.
However, the state where the passages inside of the fuel cell are closed (also known as the passage closing state or the diffusion state of the reactive gases) does not always depend on the temperature of the fuel cell. That is, even when the temperature of the fuel cell is low, the passages inside of the fuel cell may not be closed and the diffusion of the reactive gases may be in a desired state. Also, conversely, even when the temperature of the fuel cell is not very low, the fuel cell may have a closed passage and the diffusion of the reactive gases may be in an undesired state.
When the passage closing state inside the fuel cell does not depend on the temperature of the fuel cell, if the presence or the absence of a below-zero-temperature activating operation and the conditions for supplying the reactive gases are determined based on the temperature of the fuel cell 1 as in the conventional systems, the below-zero-temperature activating operation may be executed even when the activating operation for ordinary temperatures is enough. In this case, there may be an increase in the amount of the reactive gases being supplied, as well as the pressure of the gases, which may result in an undesired influence on a solid polymer electrolyte membrane of the fuel cell.